1. Field of the Invention
The invention relates to a battery parallel-operation circuit used to connect plural battery units in parallel to one another. The invention also relates to a battery system using a battery parallel-operation circuit.
2. Description of Related Art
JP2002-142353A discloses a system using parallel-connected plural battery units each of which includes one or more secondary batteries. FIG. 12 shows apparatus 900 using plural battery units connected in parallel to one another. In apparatus 900, battery units 901 to 903 are connected in parallel to one another. The output of battery units 901 to 903 drive load 910 in apparatus 900. Battery units 901 to 903 are charged by charging circuit 911 in apparatus 900.
The characteristics of the secondary batteries deteriorate with repeated charging and discharging. For this reason, in many cases, apparatus 900 using battery units 901 to 903 is configured so that each battery unit can be replaced. For instance, the user of apparatus 900 can change only battery unit 901 when necessary.